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PTI develops lightweight, foamed PET bottle/jar blow-molding process
Plastic Technologies Inc (PTI) has developed the first lightweight, foamed polyetheylene terephthalate (PET) bottle/jar blow-molding process. Marketed under the Opti brand name, the process is based on MuCell technology licensed from Trexel Inc.
The capability will now provide food and beverage brand owners with a broader range of PET container aesthetics and performance capabilities than previously possible. For example, the process enables white or silvery coloured bottles to be made without additives which can limit package recycling.
Containers also have a unique surface feel and provide tactile ‘traction’, which minimises slipping. This process also blow-molds details more prominently, which enables decorations such as embossed logos to stand out better.
The Opti bottle technology provides desirable features for those brand owners looking for a distinctive, new, visual presence, while at the same time retaining the recycling benefits that inclusion in the clear PET waste stream offers.
“White Opti bottles provide an environmentally friendly option to conventional bottles which use additives to achieve a similar tint,” said Frank Semersky, vice president, PTI. “Instead of being a contaminant to the clear recycling stream, white-foamed bottles will mold into a transparent bottle after remelting and subsequent processing.”
In addition to white or silver, blue and green hues can also be used, since those colour streams already exist in traditional PET recycling. The technology also is capable of producing bottles in a variety of pastel colours. However, these cannot be recycled as part of the clear PET stream. Containers can be made from slightly translucent to opaque depending on the desired aesthetics and performance characteristics.
Because the foam process adds stiffness, lightweighting of up to 5% is also feasible without significant loss of performance. Furthermore, the technology can produce bottles with significant light barrier characteristics –up to 95% reduction in transmitted light.
Four-step process
PTI’s Opti bottle capability is based on using the MuCell micro-cellular foam injection molding technology to mold preforms, which then can be blow-molded on conventional equipment. The bottles are made in four basic steps:
- Nitrogen is injected into the melt through the barrel on a modified preform molding machine to form a single-phase solution of polymer and gas.
- Foam is produced as cavity-fill pressure is dropped below nucleation pressure during the injection cycle.
- Foam cells expand as gas is diffused into bubbles. Processing conditions are used to control cell growth in the finished preform.
- The preforms are blow-molded on conventional, unmodified blow-molding machines to produce the foam bottles.
“Initial evidence is that at higher gas levels, foam containers can withstand hot filling without excessive shrinkage,” said Semersky. “This means that hot-fill applications are within the realm of possibility. We also can run foam bottles with a variety of barrier additives to meet shelf-life concerns.”
In addition to PET, the foam bottle technology is applicable to other resins such as polylactic acid (PLA) and polyethylene naphthalate (PEN).
Source: Plastic Technologies Inc
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